This is a request for funds to purchase an electron microscope needed for studies of tissues, cells and molecules. A Primary User Group composed of 9 principal investigators and their laboratories, totaling nearly 30 individuals, is identified. The research of these investigators is supported by over 20 separate peer-reviewed grants from the National Institutes of Health and the National Science Foundation, and 8 peer-- reviewed grants from other sources (e.g., Muscular Dystrophy Association, etc.). The research of these investigators falls into two areas: developmental neurobiology, and cellular processes of neuronal and non-neuronal cells, both at the cellular and molecular levels. The equipment will form the basis of a shared ultrastructural facility in the Department of Pathology, shared by the primary user group who are faculty members of the Departments of Pathology, Anatomy and Cell Biology, Physiology, and Biochemistry and Molecular Biophysics. This equipment is needed to accommodate new investigators (all Pi's have assumed Columbia appointments in the last three years). The facility will also relieve overcrowding in existing facilities, namely a shared EM facility jointly run by the Departments of Anatomy and Cell Biology, and Physiology, used primarily by the designated Secondary User Group. Need for this equipment is justified by the numbers of investigators requiring access to high resolution ultrastructural tools. The equipment will be maintained by trained personnel and will be available 24 hours a day to the user group. Installation and start-up costs will be borne by Columbia University.